A light-emitting device (LED) is a p-n junction diode having a characteristic in which electric energy is converted into light energy, may be produced by a compound semiconductor of Group III and Group V elements or the like on the periodic table, and may represent various colors by adjusting a composition ratio of a compound semiconductor.
In a LED, when a forward voltage is applied, electrons of an n layer are combined with holes of a p layer, and energy corresponding to band gap energy between a conduction band and a valence band may be generated, and this energy is mainly emitted in the form of heat or light, and when the energy is emitted in the form of light, the LED functions.
For example, a nitride semiconductor has received a great interest in a development field of an optical device and a high-output electronic device due to high thermal stability and wide band gap energy thereof. In particular, a blue LED, a green LED and an ultraviolet (UV) LED using the nitride semiconductor are commercialized and used widely.
Recently, the brightness problem of a light-emitting diode has significantly been improved, so that the LED is applied to various devices such as a back light unit of a liquid crystal display device, an electric signage, a display device, and home appliances, etc.
A general liquid crystal display device displays images or videos with light passing through a color filter by controlling the transmission ratio of light of a plurality of light-emitting units in which a LED is mounted and liquid crystal. The general liquid crystal display device includes a back light unit including a light source module and an optical sheet, a TFT array substrate, and a liquid crystal display panel including a color filter substrate and a liquid crystal layer. A general light source module includes a plurality of LED packages in which light-emitting chips are mounted on a lead frame substrate and a printed circuit board on which a plurality of LED packages are mounted, and further includes a driving substrate including a drive circuit for driving a light source module and a liquid crystal display panel.
Recently, high definition above an HD class and displays over 100 inches have been required, but a liquid crystal display device and an organic light-emitting display device having complex configurations that are typically used mainly, have been had difficulty in implementing display devices over 100 inches with high definition due to yield and cost.